1. Field of the Invention
The present invention relates to a mounting structure in which an EGR valve or an EGR tube is mounted to an intake manifold made of aluminum.
2. Description of the Related Art
A known EGR (exhaust gas re-circulating system) for decreasing NOx and improving the fuel consumption in an internal engine is shown in FIG. 4. In this system, an exhaust gas introduced from an exhaust manifold 1 to an EGR tub e 2 is flow controlled by an EGR valve 3 and is then returned back via an intake manifold 4 to a combustion chamber. The problem is that while the EGR valve 3 is mounted by tightening nuts 6 onto stud bolts 5 implanted to the intake manifold 4, increase in temperature by the exhaust gas at the female threads in the intake manifold 4 into which the stud bolts 5 are screwed may decline the physical strength. Particularly, when the intake manifold 4 is made of aluminum, its physical strength may be declined even to a half by a temperature of almost 250.degree. C. hence failing to maintain the axial force of holding the stud bolts 5 and causing leakage of the exhaust gas. For compensation, as shown in an enlarged primary part view of FIG. 5, a cooling water passage 4b is provided adjacent to the female threads 4a in the intake manifold 4 and is connected to water hoses 7 at the outside for supplying a cooling water to cool down the female threads 4a. This will however increase the number of relevant components, the overall weight, and thus the manufacturing cost.
In addition, as shown in FIG. 6, a mounting portion 10a of an EGR tube 10 may be joined to the intake manifold 4 made of aluminum with the use of stud bolts 5 and nuts 6. This structure also requires cooling of the female threads for the stud bolts 5 in the intake manifold 4 with cooling water.